Carburetor



Nov. 29, 1938. R. F. BRACKE 2,138,590

CARBURETOR Filed Feb. 1, 1955 Patented Nbv. 29, 1938 UNITED .ATENTOFFICE 18 Claims.

This invention relates to carburetors adapted to supply carbureted fuelto internal combustion engines and the like.

One of the objects of the invention is to pro- 5 vide an improvedcarburetor.

A further object of the invention isto provide an improved carburetor ofthe fuel lift type.

A further objectof the invention is to provide a carburetor of the fuellift type in which the degree of fuel lift vacuum is modified underidling. conditions. to provide an automatic selfcompensating idlingcontrol.

A further object of the invention is to provide an improved downdraftcarburetor.

Afurther object of the invention is to provide an improved carburetorhaving an expanding Venturi tube which automatically adjusts itself todifferent conditions of engine operation.

Other objects, advantages, and capabilities of the invention will appearfrom the following description of a preferred embodiment thereof, takenin conjunction with the accompanying drawing, which shows incross-section, a carburetor embodying my invention.

Referring to the drawing, the carburetor comprises two principalportions l and H which may suitably be castings. The upper portion l0comprises a relatively large cylindrical mouth l2 which serves for theadmission of air. The mouth i2 is provided with a spider 13 whichsupports a central hub M. The hub I4 is bored axially, the lower portionof the bore being threaded to receive the exteriorly threaded surface ofthe primary Venturi tube or nozzle 15, which is directed downwardly. Theupper end of the Venturi tube 15 is provided with a shoulder [6 whichengages the upper face of the hub I4. The hub I4 and Venturi tube areconformed to provide an annular chamber l'l around the throat of theVenturi tube. Fuel supply jets l8, which are preferably sloped inwardlyand downwardly, extend between the annular chamber I! and the throat ofthe Venturi tube l-5.

The annular chamber I1 communicates through a duct I9, which may extendthrough one of the spokes of the spider l3, with a vertical bore 20. Thelower portion of this bore 20 is enlarged to receive a dependingguidetube 2| and its intermediate portion is threaded to receive a plug22, the upper end of which is provided with a relatively large meteringorifice 23 for the passage of liquid fuel. The guide tube 2| may besecured within the lower portion of the vertical bore 20 in any suitableway. It is, however, preferred to secure the tube 2| to the casting IDby means of the plug 22, which may be provided at its lowerend with aflange which engages an inwardly extending flange at the upper end'ofthe tube 2|.

An economizer pin 24 is adapted to project upwardly through the orifice23. At its lower end the pin is secured to an inverted cup 25 which hasa sliding fit in the tube 2|. Above the cup 25 a relatively. Weak coilspring 26, of large diameter, is provided. This spring abuts against theflange at the upper end of. the tube 2! so as to tend tomove the cup 25and pin 24 downwardly. The upper end of. the pin 24 is provided with anenlarged head 2:! which is located within the orifice 23 during the partthrottle range of the carburetor, corresponding to speeds between idlingand, for example, sixty-five miles an hour. In this range the clearancebetween the head 2? and the metering opening 23 is relatively small sothat only a restricted passageway for fuel is provided. Below the head21 the pin 24 comprises a restricted portion 28, which portion islocated'within the orifice 23 when the throttle is wide open, aswill'hereinafter be described. The cup 25 is. provided with an opening29 which permits fuel to pass upwardly therethrough. The opening 29 :issufiiciently. small so that the cup 25 serves as the accelerator pump,supplying an increased amount; of fuel when the accelerator is Will beunderstood that thesev two portions of the carburetor are assembledtogether in any suitable manner, a gasket 32 being provided between thecontacting surfaces.

The lower portion of the carburetor comprises a stepped cylindrical body34 which is 10- cated in alignment with the cylindrical mouth l2. Thefuel chamber 3|, which is located below the fiat member 30 and the bore20, is located alongside the stepped cylindrical body 34. The throttlevalve 35rwhich may be a butterfly valve of the usual type, is located.within the lower narrower portion of the stepped cylindrical body 34. Asleeve 36 is slidably mounted within the cylindrical .body 34,: beingprovided with an annular bearing surface 31 whichhas-a sliding fit inthe lower portion of the stepped cylindrical body 34 and an annularbearing surface 38 of greater diameter which has a sliding fit withinthe upper enlargedportion of the stepped cylindrical body34. The sleeve36 and stepped cylindrical body 34 provide between them a chamber 39, inwhich is provided a coil spring 45 normally tending to press the sleeve35 upwardly so that its upper edge is brought into sealing engagementwith the hub l4 of the spider l3. A duct 4! extends from the chamber 39to the interior of the sleeve 35, opening thereinto preferably at apoint near the upper end of the sleeve.

The fuel chamber 3| is provided with a fioat 44 which controls a fuelinlet valve (not shown) in known manner. The bottom wall of thefuelchamber 3| is provided with an elongated vertical sleeve 45 whichreceives a rod 47 adaptedto bear upon the upper wall of the inverted cupat or near its center. The lower end of the rod rests upon an arm 45pivotally mounted on the body of the carburetor at a suitable point.Intermediate its pivotal point and the point of contact with the rod 4?,the arm 48 rests on a cam 49 which is mounted on the shank of thethrottle valve outside. the stepped cylindrical body 34. Thefcam 49 isconfigured so that when the throttle valve 35 is opened the arm 48 israised to elevate the head 27 of the pin 24 within the .metering orifice23. At-;a predetermined throttle opening the head. 2? emerges from. theorifice 23 and the clearancebetween the reduced portion 28 of the pin 24and the opening 23 provides an enlarged passage for the liquid fuel tomeet the great demand for power at high speeds. It will be noted that.the pin 24 is not positively connected to the rod 41 and that there isno necessityfor exact alignment between the rod be mounted andmaintained incoaxial relation with the opening 23. The tube 2| projectsbelow, and the sleeve 45 projects above the normal fuel level of thefuel chamber 3|, defined by'the float 44.

At one side, for example, the side opposite the fuel chamber 3|, thestepped cylindrical body 34 is provided with a solid Wall of enlargedthickness designated 55. This wall is provided with a transverse bore 5|for the accommodation of the fuel lift or booster Venturi tube 52. Theinner end of the bore5| is reduced slightly as shown at 53. The adjacentportion .of the bore 5| is threaded so as to receive the correspondinglythreaded portion'of the Venturi tube 52. On the inner side of the head54 of. the Venturi tube 52, the bore5l and the Venturi tube 52 areconformed to provide an annular passageway 55 which surrounds the throatof the Venturi tube 52 and communicates therewith through openings 55.The outer end of'thebor'e 5! is enlarged so as to receive the head 54 ofthe Venturi tube 52 and provide a chamber 57. A duct 58 connects theannular passage 55 to the upper portion of the fuel chamber 3.! A duct59 extends downwardly from the chamber 51 to a point below the The duct59 is connected by drical body 34 below the closed position of thethrottle valvei35, and preferably at a point closely adjacent saidvalve.

The effective area of the duct 30 is controlled by a needle valve52which is provided with a milled head whereby it may readily be adjusted.The wall 50 is provided with a flat outer face 54 which contains theouter end of the chamber '51. A duct extends from the fiat face 54 intothe annular chamber 39. A plate 55 is pivotally mounted on the flat face54 by means of a screw 5l a spring 58 serving to hold the plate 65against the face 54. The plate 55 is provided with a metering orifice 69adapted to register with the chamber 51 during the normal operation ofthe engine to which the carburetor is attached. The plate 65 isconnected to suitable means (not shown) for its operation in the usualmanner of operating a choke. When thus operated, the metering orifice 59is brought out of register with the chamber 5i so that the Venturi tube52 is rendered inoperative for the time being. plate 55 is provided withan opening 15 which is adapted to be brought into register with the duct55 in the choked position of the plate 65.

Inthe normal operation of the carburetor with the engine running, themetering orifice 59 is in register with the chamber 5'! and the opening15 is out of register with the duct 55, which is. consequently closed,the throttle 35 is partly open, and the rod 47 and pin 24 are slightlyelevated above the position shown in the drawing. The suction of themotor is sufficient to move the sleeve 35 downwardly somewhat away from=seated relation with the hub it of the spider. l3, so that secondary airis admitted through the mouth 12, the sleeve 35 and stepped cylindricalbody 35 into the intake manifold of the engine. Air drawn throughthe-Venturitube 52 .bythe suction of the engine creates a vacuum in, theduct 58 which is communicated to the fuel cham ber 3 I. This vacuuminthe fuelchamber effects the elevation of liquid fuel from the main fueltank inknown manner, the float 44 closing the valve (not shown). when apredetermined level is attained. In this way a. constant level of fuelis maintained in the chamber 3!.

With variations in engine suction, the vacuum The vary considerably. Theair flowing through the Venturi tube 52 impinges upon the lower end of rthe sleeve 35 which is slightly reduced below the bearing surface 3'! toprovide clearance for the passage of air downwardly towards the throttlevalve 35. This reduced portion of the sleeve tapers downwardly slightly,as shown in I the drawing. the flow of air through the Venturi tube 52and this resistance is increased at high speeds owing to the lowerposition of the sleeve .35, which results in the narrowing of thepassage between the sleeve and the wall and also increases the length ofrestricted travel between the discharge of the air at 53 until it ismixed with the main stream floating downwardly past the throttle valve35. As a consequence, the vacuum in the fuel chamber 3!, while itincreases progressively with increase of enginespeed, does not increaseat as great a rate as it would if the action. of the Venturi tube 'werenot modified in this manner;

' The suction of the engine is partly satisfied by the secondary airentering the sleeve 35 around the hub I4, and partly by the rich'mixtureof air and fuel delivered by the Venturi tube 55. primary air is drawnthrough thezVenturitube l5 by the suction of the engine and the momentumof the secondary air entering the mouth I2 imparts an initial velocityto the primary air which increases'the emciency of the Venturi tube I5.The Venturitube l5 elevates fuel through the tube 2!, the opening 29 inthe cup 25, the open- The This sleeve introduces resistance to- 23. Atgreater speeds the head 21 is above the opening 23 and a less restrictedpassageway is provided for the liquid fuel.

The suction of the engine within the sleeve 35 extends through the duct4| into the annular chamber 39 and causes a downward movement of thesleeve 36', against the action of the spring 40, proportionate to theintensity of the engine suction.

An important feature of my invention is the automatic self-compensatingidling control. In order to understand this control, it is firstnecessary to appreciate certain fundamental relationships. The amount offuel supplied by the Venturi tube or nozzle I5 is dependent both uponthe volume of airflowing through this tube and also upon the degree ofsuction existing in the fuel chamber 3|, so that by varying the degreeof suction in the fuel chamber 3| the amount of fuel supplied by theVenturi tube l5 can be varied for any given amount of air flowingtherethrough.

The degree of suction existing in the fuel chamber 3| is controlled bythe booster Venturi tube 54 and is proportional to the volume of airflowing through this booster tube. The volume of air flowing throughthis booster tube 54 in turn depends upon difference in pressure at theends of this tube, and I Vary the degree of suction existing in the fuelchamber 3| and therefore the amount of fuel supplied by the Venturi tubel5, by varying the pressure differential between the ends of the boosterVenturi tube 54. The Venturi tube 54 derives its air supply from thechamber 5'! which communicates with atmosphere through metered orifice69 which restricts the flow of air into the chamber 51. The chamber 51is also connected to that part'of the manifold on the engine side ofthrottle valve 35 by means of passageways controlled by needle valve 62.

When the throttle valve 35 is substantially open, there is very littlesuction communicated to chamber 51. by means of the passagewayscontrolled by needle valve 62, but when the throttle valve 35 is movedto idling or substantially closed position, the manifold vacuum risesand consequently the suction existing in the chamber 51 is increased,thereby decreasing the degree of suction in the fuel chamber 3| andpermitting the Venturi tube |5to supply a richer mixture. The carburetoris adjusted by means of the needle valve 52 so that a rich mixture issupplied to the engine at idling speed.

If the mixture suppliedto the engine during idling should temporarilybecome lean for any reason, such, for example, as the passage of a smallamount of vapor instead of liquid fuel to the passages l8 in the Venturitube I5, the effect of this lean mixture will be to cause the engine tospeed up slightly. This speeding up creates a higher degree of suctionin that part of the manifold on the engine side of the throttle valve,and this higher degree of suction is communicated to the chamber 51through passages 59 and 6|]. The resulting increase in suction inchamber 51 reduces the pressure drop across the Venturi tube '54 andthis .in turn reduces the degree ofsuction obtaining in the fuel chamber3|. Accordingly, fuel feeding nozzle l5 draws more fuel from fuelchamber 3| and supplies a richer mixture to the engine, thus causingitto slow down again and resume its normal idling speed.

In a similar manner my improved idling contI'O1 Wi11 compensatefortemporary increases in the richness of the mixture, bycausingcorresponding increases inthedegree of suction ex isting in thefuel chamber 3|, thereby reducing the richness of the mixture suppliedby the fuel feeding Venturi tube l5. This leaning of the mixture speedsup the rotation of the engine and reestablishes normal idling speed.

When the plate 66 is moved to choked position, the chamber 39 is put incommunication with the atmosphere through the duct 65 and opening 10.The chamber 51 is closed by the plate 55 and the Venturi tube 52 isrendered inoperative as a booster so that the degree of suctionobtaining in the fuel chamber 3| becomes equal to that existing in themixing chamber. Consequently, the suction of the engine draws a veryrich mixture through the Venturi tube l5 and ease of starting results.

Although the invention has been described in connection with thespecific details of a preferred embodiment thereof, it must beunderstood that such details are not intended to be limitative of theinvention except in so far as set forth in the accompanying claims.

Having thus described my invention, what I claim. as new and desire tosecure by Letters Patent of the United States is:

1. A downdraft carburetor comprising a stepped body, a sleeve having apair of bearing surfaces of different diameters slidable in said bodyand providing a chamber of variable capacity between said sleeve andbody, a spring tending to force said sleeve upwardly, a downwardlydirected Venturi tube mounted in the upper part of said body,

and means surrounding said Venturi tube adapted to receive the upper endof said sleeve to exclude secondary air, said sleeve having an openingestablishing communication between said chamber and a point within saidsleeve.

2. A downdraft carburetor comprising a stepped body, a sleeve having apair of surfaces of different diameters slidable in said body andproviding a chamber of variable capacity between said sleeve and body, aspring tending to force said sleeve upwardly, a downwardly directedVenturi tube mounted in the upper part of said body, means surroundingsaid Venturi tube adapted to receive the upper end of said sleeve toexclude secondary air, said sleeve having an opening establishingcommunication between said chamber and a point within said sleeve, andsaid body having an opening establishing communication between saidchamber and the atmosphere, and means adapted to be actuated to open andclose said last-mentioned opening at will.

3. A downdraft fuel lift carburetor comprising a stepped body, a sleevehaving a pair of bearing surfaces of different diameters slidable insaid body and providing a chamber of variable capacity between saidsleeve and body, a spring tending to force said sleeve upwardly, adownwardly directed Venturi tube mounted in the upper part of said body,means surrounding said Venturi tube adapted to receive the upper end ofsaid sleeve to exclude secondary air, said sleeve having an openingestablishing communication between said chamber and a point within saidsleeve and said body having an opening establishing communicationbetween said chamber and the atmosphere, a fuel lift Venturi tubedischarging into said body, and means adapted to be actuated at willeither to open the last-mentioned opening and close the fuel liftVenturi tube or to close said last-mentioned opening and open the fuellift Venturi tube. V

l. A'downdraft fuel lift carburetor comprising a stepped body, a sleevehaving a pair of bear 'ing surfaces of different diameters slidable insaid body and providing a chamber of variable capacity between saidsleeve and body, .the lower end of said sleeve being of reduced diameterto provide a clearance between itand the adjacent portion of the body, aspring tending to force said sleeve upwardly, a downwardly directedVenturi tube mounted in the upper part of said body, means surroundingsaid Venturi tube adapted toreceive the upper end of said sleeve toexclude secondary air, said sleeve having an opening establishingcommunication between said chamber and a point within said sleeve andsaid body having an opening establishing communication between saidchamber and the atmosphere, a fuel lift Venturi tube discharging intosaid'body the discharge from which is adapted to impinge against saidreduced portion of the sleeve so that resistance to flow through thefuel lift Venturi tube is increased by the downward movement of thesleeve, and means adapted to be actuated at will either to open the lastmentioned opening and close the fuel lift Venturi tube or to close saidlast mentioned opening and open the fuel lift Venturi tube.

5. A carburetor comprising upper and lower portions secured together, afuel chamber in the lower portion having a sleeve projecting upwardlyabove the fuel level, an actuating rod projecting through said sleeve, atube projecting from the upper portion to below the fuel level andhaving a fuel outlet at its upper end, said tube and sleeve being insubstantial alignment, and a perforated piston in said tube adapted tobe actuated by said rod. i

6. A carburetor'comprising upper and lower portions secured together, afuel chamber in the lower portion having a sleeve projecting upwardlyabove the fuel level, an actuating rod projecting through said sleeve, atube projecting from the upper portion to below the fuel level andhaving a fuel outlet at its upper end, a perforated piston in said tubeadapted to be'actuated by said rod, and a member carried by said pistonand extending into said fuel outlet adapted to control the effectivesize thereof in accordance with the position'of the piston.

7; A carburetor comprising upper and lower portions secured together andhaving a throttle valve, a fuel chamber in the lower portion, a tubeprojecting downwardly from the upper portion to below the fuel level,and having a fuel outlet at its upper end, a piston in said tube adaptedto be moved progressively with the throttle Valve, and means carried bythe piston adapted to project through the fuel outlet to modify theeffective size thereof in accordance with the throttle valve position.

8. In a carburetor, incombination, an accelerator pump having aperforated piston adapted to provide an enhanced supply of fuel on rapidacceleration, said fuel passing through said piston and through ametering orifice, and an economizer element rigidly carried by saidpiston and projecting through saidorifice to control the effective areathereof in accordance with throttle position.

9. A fuel lift carburetor comprising a main Venturi tube, a fuel liftVenturi tube, a mixing chamber into which said Venturi tubes deliver, a

I valve responsive to suction in the mixing chamher and adapted toimpede the flow through the fuel lift Venturi tube to a degreedependingupon from the mouth of the fuel lift Venturi tube to the engine side ofthe throttle valve, and adjustable means adapted to control the flowthrough said duct.

10. A fuel lift carburetor comprising a fuel chamber, a main Venturitube, a fuel lift Venturi tube, ducts connecting the throats thereof tothe fuel chamber, a mixing chamber intowhich the Venturi tubes deliver,a throttle valve controlling the outlet from said mixing chamber, a ductextending from the outer end of said fuel lift Venturi tube to theengine side of'the throttle valve, and a screw for adjusting the flowthrough the last-mentioned duct. 7 i

11. A carburetor comprising a pair of complementary sections securedtogether, a fuel chamber in one section having a sleeve projectingupwardly above the fuel level in said chamber, an actuating rodprojecting through said sleeve and guided thereby, a tube carried'by theother sectionand projecting into said chamber to a point below the fuellevel therein, said tube telescoping the upper end of said sleeve andhaving a fuel outlet at its upper end, and pump means guided V by saidtube, said means and said rod having surfaces conformed to provide asatisfactory, operative connection therebetween irrespective ofmisalignment between said tube and said sleeve.

12. A fuel lift carburetor comprising a main Venturi tube, a fuel liftVenturi tube, a mixing chamber into which said Venturi tubes deliver,

subatmospheric pressure in said chamber whereby fuel is drawn thereintofrom a main fuelsupply tank located at a distance from said cham her, amixing chamber into which said Venturi tubes deliver, a throttle valvein said mixing chamber, and a by-pass operable at nearly closed throttlepositions for reducing the effectiveness of the fuel lift Venturi tube.i

14. A fuel lift carburetor comprising a main Venturi tube, a fuelchamber from which said main Venturi tube is supplied, a fuel liftVenturi tube for creating a subatmospheric pressure in said fuel chamberwhereby fuel is drawn thereinto'from a main fuel supply tank, a mixing'chamber into which said Venturi tubes deliver, a throttle valve in saidmixing chamber, and a duct communicating between the inlet of the fuellift Venturi tube and the engine side of the throttle valve.

15. A fuel lift carburetor comprising a main Venturi tube, a fuelchamber from which said Venturi tube is supplied, a fuel lift Venturitube for creating a subatmospheric pressure in said chamber whereby-fuelis drawn thereinto from a main fuel supply tank, a mixing chamber intowhich said Venturi tubes deliver, a valve responsive tosuction in themixing chamber and adapted to impede the flow through the fuel liftVenturi tubeto a degree depending upon said su"- tion, a throttle valvecontrolling the outlet from said mixing chamber, and a duct extendingfrom the inlet of the fuel lift Venturi tube to the engine side'of thethrottle valve.' 1 T 16. A carburetor comprising upper and lowerportions secured together, a fuel chamber in the lower portion having apart projecting upwardly above the fuel level, an actuating rodprojecting through said part, a second part projecting from the upperportion to a point below the fuel level and providing a cylinder, saidcylinder having a fuel outlet at its upper end, said parts being insubstantial alignment, and a perforated piston in said cylinder adaptedto be actuated by said rod.

17. A fuel lift carburetor comprising a main Venturi tube, a fuel liftVenturi tube, a mixing chamber into which said Venturi tubes deliver, athrottle valve in said mixing chamber, a metering orifice limiting theadmission of atmospheric air to said fuel lift Venturi tube, means forvarying the size of said orifice, a chamber located between said orificeand the inlet to said last mentioned Venturi tube, and a ductestablishing communication between said last mentioned chamber and theengine side of the throttle valve.

18. A fuel lift carburetor comprising a fuel chamber, a main Venturitube supplied from said chamber, a fuel lift Venturi tube for creatingsub-atmospheric pressure in said chamber, whereby fuel is drawnthereinto from a main fuel supply tank located at a distance from saidchamber, a mixing chamber into which said Venturi tubes deliver, athrottle valve in said mixing chamber, a by-pass operable at nearlyclosed throttle positions for reducing the effectiveness of said fuellift Venturi tube, and other means operable at open throttle positionsfor reducing the effectiveness of the fuel lift Venturi tube.

ROBERT F. BRACKE.

